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Search Results: 1 - 10 of 32403 matches for " Peter Heger "
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Loss of the insulator protein CTCF during nematode evolution
Peter Heger, Birger Marin, Einhard Schierenberg
BMC Molecular Biology , 2009, DOI: 10.1186/1471-2199-10-84
Abstract: While orthologs for other insulator proteins were absent in all 35 analysed nematode species, we find orthologs of CTCF in a subset of nematodes. As an example for these we cloned the Trichinella spiralis CTCF-like gene and revealed a genomic structure very similar to the Drosophila counterpart. To investigate the pattern of CTCF occurrence in nematodes, we performed phylogenetic analysis with the ZF protein sets of completely sequenced nematodes. We show that three ZF proteins from three basal nematodes cluster together with known CTCF proteins whereas no zinc finger protein of C. elegans and other derived nematodes does so.Our findings show that CTCF and possibly chromatin insulation are present in basal nematodes. We suggest that the insulator protein CTCF has been secondarily lost in derived nematodes like C. elegans. We propose a switch in the regulation of gene expression during nematode evolution, from the common vertebrate and insect type involving distantly acting regulatory elements and chromatin insulation to a so far poorly characterised mode present in more derived nematodes. Here, all or some of these components are missing. Instead operons, polycistronic transcriptional units common in derived nematodes, seemingly adopted their function.Chromatin insulation plays a profound role in regulating gene expression and is mediated by the binding of insulator proteins to specific DNA sequence elements. So far, in only a limited number of organisms insulator function has been demonstrated: in yeast [1-3], sea urchin [4,5], Drosophila (e. g. [6,7]), and vertebrates (e. g. [8,9]). D. melanogaster and vertebrates are the only metazoan systems where insulator binding proteins have been identified. In Drosophila, Suppressor of Hairy Wing [Su(Hw)], Boundary Element Associated Factors (BEAF-32A and BEAF-32B), Zeste-white 5 (Zw5), GAGA Binding Factor (GAF), and, most recently, CTCF (dCTCF) have been described as functional insulator proteins. In contrast, there is onl
Conservation of MAP kinase activity and MSP genes in parthenogenetic nematodes
Peter Heger, Michael Kroiher, Nsah Ndifon, Einhard Schierenberg
BMC Developmental Biology , 2010, DOI: 10.1186/1471-213x-10-51
Abstract: We investigated two key elements of oocyte-to-embryo transition, MSP expression and MAP kinase signaling, in two parthenogenetic nematodes and their close hermaphroditic relatives. While activated MAP kinase is present in all analysed nematodes irrespective of the reproductive mode, MSP expression differs. In contrast to hermaphroditic or bisexual species, we do not find MSP expression at the protein level in parthenogenetic nematodes. However, genomic sequence analysis indicates that functional MSP genes are present in several parthenogenetic species.We present three alternative interpretations to explain our findings. (1) MSP has lost its function as a trigger of MAP kinase activation and is not expressed in parthenogenetic nematodes. Activation of the MAP kinase pathway is achieved by another, unknown mechanism. Functional MSP genes are required for occasionally emerging males found in some parthenogenetic species. (2) Because of long-term disadvantages, parthenogenesis is of recent origin. MSP genes remained intact during this short intervall although they are useless. As in the first scenario, an unknown mechanism is responsible for MAP kinase activation. (3) The molecular machinery regulating oocyte-to-embryo transition in parthenogenetic nematodes is conserved with respect to C. elegans, thus requiring intact MSP genes. However, MSP expression has been shifted to non-sperm cells and is reduced below the detection limits, but is still sufficient to trigger MAP kinase activation and embryogenesis.Throughout the animal kingdom, female gametes interrupt their development during oogenesis at various stages of meiosis. In response to external stimuli, this arrest is released, and oocyte maturation can take place. Then oocytes resume meiotic divisions, ovulate and get competent for fertilisation.An important step during oocyte maturation of all animals is MAP kinase activation (reviewed in [1-3]). MAP kinases are ubiquitous serine-threonine protein kinases expressed
Matej Brestensky,Soňa Nitrayová,Peter Patrá?,Jaroslav Heger
Journal of Microbiology, Biotechnology and Food Sciences , 2012, DOI: 13385178
Abstract: We used 6 cannulated gilts (initial BW 34.8 ± 0.7 kg) fitted with ileal T-cannula in terminal ileum for estimation ileal digestibility (ID) of nitrogen (N) and amino acids (AA) in sorghum. Animals were fed twice a day with tested diet in daily amount 75-80 g.kg- 0.75. Water was offered ad libitum. The tested sorghum was only protein source in the diet. After 6 days during which the animals were fed with experimental diet followed 24 hours collection of ileal digesta. We used Cr2O3 as indigestible marker in amount 0.3 % of diet. We calculated apparent and true ileal digestibility of AA and N using analytic estimated values of N, Cr2O3, and AA. True ID of AA in sorghum ranged between 64.8 % (glycine) and 88.6 % (tyrosine) (P<0.05). Ileal digestibility for lysine was 72.8 % ± 2.1. True ileal digestibility for essential amino acids (80.7 % ± 2.1) was similar in comparison with true ileal digestibility of nonessential amino acids (79.7 % ± 2.4). Apparent ileal digestibility of essential and nonessential AA was 73.6 % ± 2.1 and 71.4 % ± 2.4 respectively. Sorghum is full-value nutritional source for pigs comparable with other feeds.
Peter Patrá?,Soňa Nitrayová,Matej Brestensky,Jaroslav Heger
Journal of Microbiology, Biotechnology and Food Sciences , 2012, DOI: 13385178
Abstract: The effect of enzyme xylanase derived from Trichoderma longibrachiatum supplemented to a rye-based diet on apparent ileal digestibility of amino acids and non-starch polysaccharides constituting sugars was studied. Enzymes supplementation at 200 mg.kg 1 increased (P 0.05) the digestibility of total amino acids from 67.1 to 70.8. When the dietary concentration of enzyme increased from 0 to 100 mg.kg-1, the ileal digestibility of the NSP constituents gradually increased as well. No further increase was observed with the supplementation level of 200 mg.kg-1. The improvement in the digestibility of arabinose and xylose (685%, P 0.05) was much higher in comparison with remaining sugars (110%, P 0.05). The apparent ileal digestibility of galactose was positively influenced by xylanase but it remained negative in all dietary treatments, presumably due to the high concentration of galactose in endogenous secretions. It is concluded that xylanase effectively degrades non-starch polysaccharides in upper digestive tract and marginally improves amino acid availability in young pigs.
Relaciones entre lo teórico y lo empírico en la dialectología
Klaus Heger
Lexis , 1980,
Abstract: No presenta resúmen
La semántica lingüística
Klaus Heger
Lexis , 1981,
Abstract: El artículo no presenta resumen.
Assessment of tissue oxygen saturation during a vascular occlusion test using near-infrared spectroscopy: the role of probe spacing and measurement site studied in healthy volunteers
Rick Bezemer, Alexandre Lima, Dean Myers, Eva Klijn, Michal Heger, Peter T Goedhart, Jan Bakker, Can Ince
Critical Care , 2009, DOI: 10.1186/cc8002
Abstract: StO2 was non-invasively measured in the forearm and thenar in eight healthy volunteers during 3-minute VOTs using two InSpectra tissue spectrometers equipped with a 15 mm probe or a 25 mm probe. VOT-derived StO2 traces were analyzed for base-line, ischemic, reperfusion, and hyperemic parameters. Data were categorized into four groups: 15 mm probe on the forearm (F15 mm), 25 mm probe on the forearm (F25 mm), 15 mm probe on the thenar (T15 mm), and 25 mm probe on the thenar (T25 mm).Although not apparent at baseline, probe spacing and measurement site significantly influenced VOT-derived StO2 variables. For F15 mm, F25 mm, T15 mm, and T25 mm, StO2 ownslope was -6.4 ± 1.7%/minute, -10.0 ± 3.2%/minute, -12.5 ± 3.0%/minute, and -36.7 ± 4.6%/minute, respectively. StO2 upslope was 105 ± 34%/minute, 158 ± 55%/minute, 226 ± 41%/minute, and 713 ± 101%/minute, and the area under the hyperemic curve was 7.4 ± 3.8%·minute, 10.1 ± 4.9%·minute, 12.6 ± 4.4%·minute, and 21.2 ± 2.7%·minute in these groups, respectively. Furthermore, the StO2 parameters of the hyperemic phase of the VOT, such as the area under the curve, significantly correlated to the minimum StO2 during ischemia.NIRS measurements in combination with a VOT are measurement site-dependent and probe-dependent. Whether this dependence is anatomy-, physiology-, or perhaps technology-related remains to be elucidated. Our study also indicated that reactive hyperemia depends on the extent of ischemic insult.It is now well established that tissue oxygen utilization and regional microcirculatory oxygen transport properties are severely affected during sepsis and shock [1-9]. To assess and identify these metabolic and microcirculatory alterations non-invasively, near-infrared spectroscopy (NIRS) has recently been applied to measure the behavior of tissue oxygen saturation (StO2). Besides observation of steady-state values, a vascular occlusion test (VOT) has been introduced for the measurement of tissue oxygen consumption and o
Metallicity-Dependent Galactic Isotopic Decomposition for Nucleosynthesis
Christopher West,Alexander Heger
Physics , 2012, DOI: 10.1088/0004-637X/774/1/75
Abstract: All stellar evolution models for nucleosynthesis require an initial isotopic abundance set to use as a starting point. Generally, our knowledge of isotopic abundances of stars is fairly incomplete except for the Solar System. We present a first model for a complete average isotopic decomposition as a function of metallicity. Our model is based on the underlying nuclear astrophysics processes, and is fitted to observational data, rather than traditional forward galactic chemical evolution modeling which integrates stellar yields beginning from big bang nucleosynthesis. We first decompose the isotopic solar abundance pattern into contributions from astrophysical sources. Each contribution is then assumed to scale as a function of metallicity. The resulting total isotopic abundances are summed into elemental abundances and fitted to available halo and disk stellar data to constrain the model's free parameter values. This procedure allows us to use available elemental observational data to reconstruct and constrain both the much needed complete isotopic evolution that is not accessible to current observations, and the underlying astrophysical processes. Our model finds a best fit for Type Ia contributing \simeq 0.7 to the solar Fe abundance, and and Type Ia onset occurring at [Fe/H]\simeq -1.2.
The Evolution of Surface Parameters of Rotating Massive Stars
Norbert Langer,Alexander Heger
Physics , 1997,
Abstract: We summarize the present status of the predictions of massive star models for the evolution of their surface properties. After discussing luminosity, temperature and chemical composition, we focus on the question whether massive stars may arrive at critical rotation during their evolution, either on the main sequence or in later stages. We find both cases to be possible and briefly discuss observable consequences.
B[e] supergiants: What is their evolutionary status?
N. Langer,A. Heger
Physics , 1997,
Abstract: In this paper, we investigate the evolutionary status of B[e]~stars from the point of view of stellar evolution theory. We try to answer to the question of how massive hot supergiants --- i.e. evolved stars --- can be capable of producing a circumstellar disk. We find and discuss three possibilities: very massive evolved main sequence stars close to critical rotation due to their proximity to their Eddington-limit, blue supergiants which have just left the red supergiant branch, and single star merger remnants of a close binary system. While the latter process seems to be required to understand the properties of the spectroscopic binary R4 in the LMC, the other two scenarios may be capable of explaining the distribution of the B[e] stars in the HR~diagram. The three scenarios make different predictions about the duration of the B[e]~phase, the time integrated disk mass and the stellar properties during the B[e]~phase, which may ultimately allow to distinguish them observationally.
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